JP7683564B2 - Vehicle control device - Google Patents

Description

This invention relates to a control device for a vehicle equipped with an antilock braking system (ABS).

If an earthquake or other event occurs while a vehicle is in motion that renders it unsafe to drive, it is necessary for the vehicle to be stopped quickly and for the occupants to evacuate. For example, Patent Document 1 discloses a device that activates the brakes and unlocks the vehicle doors when the vehicle's vertical acceleration is equal to or greater than a predetermined threshold, allowing the occupants to evacuate quickly. Patent Document 2 discloses a vehicle drive control device that variably sets overtaking drive control depending on the situation, allowing safe overtaking even in an overtaking restricted environment. Patent Document 2 discloses that the overtaking restricted environment includes an emergency earthquake warning, and that the brake control device that brakes the vehicle includes an ABS that controls the brake device to suppress or release wheel lock.

JP 2007-179096 A JP 2016-002893 A

The braking force generated by the wheels varies depending on the load of the wheels against the road surface, so if the vehicle body moves up and down due to an earthquake or the like, the braking distance from when the brakes are applied until the vehicle stops may become longer. In that case, if the ABS, which detects that the wheels are locked and adjusts the braking torque of the wheels to suppress wheel locking, is activated, the braking distance of the vehicle may become longer. For example, when the load of the wheels is reduced due to the vertical movement of the vehicle, the wheels may lock even if the braking torque is reduced by the ABS. In that case, the braking torque may be further reduced to release the lock. However, the load of the wheels returns to the original state or increases immediately thereafter, resulting in insufficient braking force of the wheels. When the load of the wheels changes unexpectedly in this way, the ABS may not operate correctly, and the braking force required to brake the vehicle may be insufficient. As a result, there is a risk that the braking distance of the vehicle may be extended due to the activation of the ABS. Such technical issues are not taken into consideration in Patent Document 1 and Patent Document 2, and there is room for improvement.

This invention was made with a focus on the above technical problem, and aims to provide a vehicle control device that can prevent the braking distance from increasing even if a vehicle equipped with an ABS applies the brakes suddenly when the ground load between the wheels and the road surface changes unexpectedly.

To achieve the above object, the present invention provides a control device for a vehicle equipped with wheels, a brake device that applies a braking torque to the wheels, and an anti-lock brake system that controls the braking torque of the brake device so that the slip ratio of the wheels relative to the road surface becomes a predetermined reference target slip ratio, the control device further comprising a controller that controls the brake device and the anti-lock brake system, the controller having an earthquake determination unit that detects the occurrence of an earthquake, and configured to prohibit operation of the anti-lock brake system or to set a corrected target slip ratio greater than the reference target slip ratio and activate the anti-lock brake system when the earthquake determination unit detects the occurrence of an earthquake.

The vehicle control device of this invention can prevent or suppress an increase in the vehicle's braking distance caused by the ABS being activated when an unexpected change in the ground load between the road surface and the wheels occurs. Therefore, when an earthquake occurs, the vehicle can be stopped quickly and the occupants can take evacuating action quickly.

1 is a diagram showing a vehicle equipped with a control device according to an embodiment of the present invention. 4 is a flowchart showing an example of control executed by a control device in the embodiment of the present invention. 6 is a flowchart showing another example of control executed by the control device in the embodiment of the present invention. 4A is a map showing the relationship of the wheel braking force to the wheel slip ratio, and FIG. 4B is a map showing the relationship of the wheel lateral force to the wheel slip ratio. 10 is a flowchart showing yet another example of control executed by the control device in the embodiment of the present invention.

The vehicle in this embodiment of the invention is a vehicle equipped with an anti-lock brake system (ABS) that controls the brake device to prevent or suppress the wheels from locking when the driver suddenly brakes while the vehicle is traveling. Figure 1 shows a schematic diagram of a vehicle Ve configured in this way. As shown in Figure 1, the vehicle Ve is equipped with a driving force source 1, a brake device 2, wheels 3, an ECU (electronic control unit) 4, a detection unit 5, etc.

The driving force source 1 outputs torque to drive the wheels 3, i.e., torque for generating driving force for the vehicle Ve. As an example, the driving force source 1 may have either a conventionally known engine (internal combustion engine) or a motor-generator, or may have both.

The brake device 2 is a device that brakes the vehicle Ve by outputting a torque that brakes the wheels 3. The brake device 2 is provided on each of the front and rear wheels 3 of the vehicle Ve. The brake device 2 is a device similar to a conventionally known brake device 2, and is, for example, a friction brake such as a disk brake, drum brake, or powder brake, and is configured to generate a friction force by hydraulic pressure or electromagnetic force to generate a braking force in a direction to stop the rotation of each wheel 3. For example, in the case of a drum brake, a piston attached to a wheel cylinder is operated by hydraulic pressure generated in a master cylinder, and the piston is configured to transmit a braking torque to the wheel 3 by the friction force generated when a brake shoe with a friction material is pressed against a brake drum that rotates together with the wheel 3. In addition, each wheel 3 is provided with a wheel speed sensor 5a for detecting the wheel speed, which is the rotation speed of each wheel. The brake device 2 is configured so that the magnitude of the braking force output is determined according to the depression angle of the brake pedal operated by the driver.

This ECU 4 corresponds to the "controller" in this embodiment of the invention, and is mainly composed of a microcomputer, for example, and is configured to perform calculations using data input from the detection unit 5 and pre-stored data, and to output a control command signal based on the calculation results. The input data includes, for example, the wheel speed, the rotation speed of the driving force source 1, and the oil pressure to the brake device 2. The ECU 4 also includes an ABS-ECU 4a and an earthquake determination unit 4b.

The ABS-ECU 4a is an ECU 4 for activating the ABS. For example, if the braking torque of the brake device 2 suddenly increases and the wheels 3 lock, an electrical signal is output to activate an ABS actuator (not shown) to control the hydraulic pressure in the wheel cylinders and adjust the braking force of the brakes. The ABS actuator is an electromagnetic control valve that operates in response to the operation of the ABS. The ABS actuator is provided, for example, between the master cylinder and the wheel cylinder, and adjusts the hydraulic pressure from the master cylinder to the wheel cylinders to adjust the braking force generated on the wheels 3.

The ABS is a conventionally known system that prevents or suppresses the wheels 3 from locking and slipping when a large braking force is required quickly due to a sudden brake operation by the driver. As an example, the ABS detects the locked state of the wheels 3 using the wheel speed sensor 5a, and when it detects that the wheels 3 are locked, it controls by reducing the brake pressure on the locked wheels 3 so that the wheels 3 grip the road surface. At that time, the vehicle speed is calculated from the wheel speed of each wheel 3, and the slip ratio of the wheels 3 is calculated based on the deviation between the vehicle speed and the wheel speed. The ABS sets a target value for the slip ratio so that the wheels 3 do not lock or so that the wheels 3 are unlocked, and controls the hydraulic pressure for the brake device 2 so that the wheels 3 rotate at a target speed based on the target slip ratio.

The earthquake determination unit 4b determines the occurrence of an earthquake based on data acquired by the detection unit 5 and external notifications. This determination of the occurrence of an earthquake may be performed by a conventionally known control, such as when an emergency earthquake warning is acquired, or the control disclosed in JP 2014-153750 A that determines the occurrence of an earthquake based on a change in the acceleration of the vehicle and its duration, or the control disclosed in JP 2008-224353 A that determines the occurrence of an earthquake based on the difference between the amount of movement and attitude of the vehicle based on an image captured by an on-board camera and the amount of movement and attitude of the vehicle based on a sensor of the vehicle.

The detection unit 5 is a device or apparatus for acquiring various data and information required for controlling the vehicle Ve. In addition to the wheel speed sensor 5a described above, the detection unit 5 includes a vehicle speed sensor 5b for detecting the vehicle speed from the rotation speed of the wheels 3, an angular velocity sensor 5c for detecting the angular velocity of the vehicle body, a brake sensor 5d for detecting the amount of operation (opening degree) of a brake pedal (not shown), an acceleration sensor 5e for detecting the acceleration of the vehicle Ve, and a master cylinder pressure sensor 5f for detecting the hydraulic pressure acting on the master cylinder of the brake device 2. The detection unit 5, ECU 4, and ABS actuator thus configured are electrically connected to each other, for example, by a CAN (Controller Area Network) or a wire harness, and output an electrical signal corresponding to the detected value or calculated value as detection data to the ECU 4.

Figure 2 shows a flowchart that is an example of the control executed by the ECU 4. First, in this flowchart, as shown in Figure 2, it is determined in step S1 that an earthquake has occurred. The occurrence of an earthquake is determined, for example, by receiving the above-mentioned emergency earthquake warning with a receiver (not shown) or by observing initial tremors.

If it is determined in step S1 that an earthquake will occur, the process proceeds to step S2. In step S2, it is determined whether or not an earthquake has actually occurred based on step S1. An earthquake actually occurring here means, for example, that the seismic intensity or magnitude is greater than a predetermined value, or that a major earthquake is occurring. For example, as described above, it is determined that the waveform indicating the change in acceleration in the forward/backward, left/right, and up/down directions of the vehicle Ve is a change specific to an earthquake, or that there is a change specific to an earthquake based on the amount of movement and attitude of the vehicle Ve based on the image processing of the onboard camera and the data detected by the detection unit 5. For example, it may be determined that an earthquake has occurred when any of the three judgments, including the emergency earthquake warning, or two or more of the three judgments are established. It may also be determined that the vehicle body vibrates relatively significantly in the up/down direction due to the earthquake, or that the earthquake is of such a scale that the vehicle Ve needs to be stopped.

If an affirmative determination is made in step S2 due to the occurrence of an earthquake, the process proceeds to step S3. If the process proceeds to step S3, operation of the ABS is prohibited. In other words, if an affirmative determination is made in step S2, the driver or other person may swiftly apply the brakes to prevent a traffic accident or to evacuate passengers, which may result in the wheels 3 being suddenly braked and locked. Then, the ABS is about to be activated to prevent the wheels 3 from locking. On the other hand, as described above, there is a possibility that the braking distance of the vehicle Ve may be lengthened by the activation of the ABS due to an unexpected fluctuation in the ground load. To prevent or suppress this, operation of the ABS is prohibited in step S3.

On the other hand, if a negative determination is made in step S2 because none of the three determinations are true, the process proceeds to step S4. In other words, if a determination is made in step S2 that an earthquake has not occurred, the process proceeds to step S4. If an earthquake has not occurred, unexpected fluctuations in ground load are unlikely to occur, so even if the ABS is activated, the braking distance of the vehicle Ve is unlikely to be extended. Therefore, in such a case, the process proceeds to step S4, and this flowchart ends without prohibiting the activation of the ABS.

The control device for the vehicle Ve configured in this manner determines that an earthquake has occurred using an emergency earthquake warning, on-board sensors, or on-board cameras. If the scale or size of the detected earthquake predicts that the ground load of the wheels 3 on the road surface will fluctuate relatively significantly, the control device is configured to prohibit operation of the ABS. This makes it possible to prevent or suppress a situation in which the braking distance of the vehicle Ve is extended due to the ABS being activated by an unexpected fluctuation in the ground load between the road surface and the wheels 3. Therefore, when an earthquake occurs, the vehicle Ve can be stopped quickly, and the occupants can quickly take evacuation action.

Next, another example of the control executed by the ECU 4 in the embodiment of the present invention will be described with reference to Figures 3 and 4. Note that in the flowcharts of the other examples described below, steps similar to those already described will be given the same reference numerals, and their description will be omitted or simplified.

As shown in FIG. 3, in the flowchart of the other example, similar to the flowchart shown in FIG. 2, in step S1, it is determined that an earthquake has occurred. If it is determined that an earthquake has occurred, the process proceeds to step S2, where it is determined that an earthquake is currently occurring. If an earthquake is currently occurring, and therefore the determination is affirmative in step S2, the process proceeds to step S5.

In step S5, the target slip ratio of the wheel 3 when the ABS is activated is increased. That is, the first target slip ratio B1 is set, which is a value larger than the reference target slip ratio B0 of the wheel 3 that is initially set when the ABS is activated, and corresponds to the corrected target slip ratio in the embodiment of the present invention. As shown in FIG. 4(a) and FIG. 4(b), the braking force of the wheel 3 increases as the slip ratio increases up to a certain level. In contrast, the lateral force, which is a force perpendicular to the central plane of the wheel 3, decreases as the slip ratio of the wheel 3 increases. That is, the braking force and lateral force of the wheel 3 are substantially inversely proportional to the slip ratio of the wheel 3. Therefore, when the ABS is activated, the reference target slip ratio B0 of the wheel 3 is calculated in a range where the braking force and lateral force are best balanced by experiments, and the brake device 2 is controlled based on the reference target slip ratio B0. On the other hand, even if the ABS set in this way is activated, the braking distance of the vehicle Ve may be extended due to unpredictable external factors such as earthquakes, as described above.

Therefore, in step S5, if an earthquake occurs, the target slip ratio at the time of ABS activation is increased. Specifically, as shown in FIG. 4(a), the setting range of the target slip ratio is changed from a predetermined setting range R1 to a range R2 set so that the braking force of the wheel 3 is increased. As shown in FIG. 4(a), in the setting range R1 of the reference target slip ratio B0, if the ground load increases or there is no change in the ground load, there is almost no difference in the minimum and maximum braking forces generated at the wheel 3 when the wheel 3 is locked and when the ABS is activated. On the other hand, when the ground load decreases and the ABS is activated, the minimum braking force generated at the wheel 3 is smaller than when the wheel 3 is locked.

In contrast, in the setting range R2 of the first target slip ratio B1, as shown in FIG. 4(a), the target slip ratio is set so that when the ground load decreases, the minimum braking force of the wheel 3 generated when the ABS is activated is approximately the same as the minimum braking force of the wheel 3 generated when the wheel 3 is locked. Therefore, when the wheel 3 is locked, the average value of the braking force of the wheel 3 from braking to stopping is close to the minimum braking force when the wheel 3 is locked, whereas when the ABS is activated, the average value from braking to stopping is larger than when the wheel 3 is locked, since it fluctuates appropriately within the above-mentioned range.

As shown in FIG. 4(b), the lateral force at wheel 3 decreases by increasing the setting range of the target slip ratio for wheel 3. Therefore, the above-mentioned control is executed when the ground load between the road surface and wheel 3 fluctuates due to an unpredictable factor such as an earthquake, and there is a possibility that the braking distance may be extended by activating the ABS. In other words, this is an emergency measure, and is executed only when it is determined that the braking force of vehicle Ve should take priority. This flowchart ends once the target slip ratio for wheel 3 when the ABS is activated has been set to the first target slip ratio B1.

If the negative determination is made in step S2 because no earthquake has occurred, the process proceeds to step S6. In step S6, the target slip ratio when the ABS is activated is not changed from the setting range R1 of the reference target slip ratio B0. If the brake pedal is quickly depressed in a state in which no earthquake has occurred, the ABS with the reference target slip ratio B0 set is activated, thereby maintaining a high braking force on the wheel 3 while suppressing a decrease in the lateral force of the wheel 3. Therefore, it is possible to execute control that shortens the braking distance of the vehicle Ve while also ensuring the stability of the vehicle Ve.

According to the control in this other example configured as above, when an earthquake occurs, the target slip ratio for the wheel 3 when the ABS is activated is set to a first target slip ratio B1, the setting range of which is larger than the range for the reference target slip ratio B0. In the setting range of the first target slip ratio B1, the minimum braking force for the wheel 3 is approximately the same as the minimum braking force when the wheel 3 is locked, so the average value of the braking force generated from the brake operation until the vehicle is stopped is high. Therefore, when an earthquake occurs, the vehicle Ve can be stopped quickly while preventing the wheel 3 from locking.

Next, another example of the control executed by the ECU 4 in the embodiment of the present invention will be described with reference to FIG. 5. In the flowchart of the further example described below, step members similar to those already described will be given the same reference numerals, and their description will be omitted or simplified.

In the flowchart shown in FIG. 4, if the answer to step S2 is affirmative because an earthquake is currently occurring, the process proceeds to step S7. In step S7, it is determined whether the current speed of the vehicle Ve is greater than a predetermined first vehicle speed. This first vehicle speed is set to a relatively high vehicle speed and is determined mainly according to the lateral force of the wheel 3 in the setting range R1 of the reference target slip ratio B0 when the ABS is activated. That is, as described above, as the slip ratio of the wheel 3 increases, the lateral force of the wheel 3 decreases, and the stability of the vehicle Ve decreases accordingly. The effect of the decrease in the stability of the vehicle Ve on the vehicle Ve increases as the vehicle speed increases, so the first vehicle speed is determined taking this effect into account. If the vehicle speed is greater than the first vehicle speed and the answer to step S7 is affirmative, the process proceeds to step S8, and the operation of the ABS is permitted.

If the ABS is permitted to operate in step S8, the process proceeds to step S9. In step S9, the target slip ratio of the ABS is set from the reference target slip ratio B0 to the second target slip ratio B2. The setting range of this second target slip ratio B2 is a value larger than the setting range R1 of the reference target slip ratio B0 during ABS operation that is initially set, and is determined based on the braking force and lateral force of the wheel 3 described above. If the vehicle speed is larger than the first vehicle speed, prohibiting the operation of the ABS may result in an excessive decrease in the lateral force of the wheel 3, which may affect the stability of the vehicle Ve. To prevent such a situation, the second target slip ratio B2 is set to a slip ratio that can suppress the decrease in vehicle stability due to the decrease in the lateral force of the wheel 3 while ensuring the braking force of the wheel 3. Once the target slip ratio during ABS operation is set to the second target slip ratio B2, this flowchart is temporarily terminated.

On the other hand, if the vehicle speed is equal to or lower than the first vehicle speed in step S7, the process proceeds to step S10. In step S10, it is determined whether the vehicle speed is higher than the second vehicle speed. This second vehicle speed is set according to the lateral force of the wheels 3, like the first vehicle speed. Specifically, although the second vehicle speed is equal to or lower than the first vehicle speed, it is set to a vehicle speed at which it is possible to determine that the lateral force of the wheels 3 can be reduced and the brake device 2 can be controlled to prioritize braking force. In other words, the second vehicle speed is set to a vehicle speed at which it is possible to determine whether or not the reduction in the lateral force of the wheels 3 due to prohibition of ABS operation can be tolerated. If the vehicle speed is higher than the second vehicle speed and therefore the determination in step S10 is affirmative, the process proceeds to step S11, and ABS operation is permitted.

If ABS operation is permitted in step S11, the process proceeds to step S12. In step S12, the target slip ratio of the ABS is set to a third target slip ratio B3. This third target slip ratio B3 is set to a value greater than the second target slip ratio B2. In other words, when the vehicle speed is equal to or less than the first vehicle speed but greater than the second vehicle speed, prohibiting operation of the ABS may result in an excessive decrease in the lateral force of the wheel 3. The third target slip ratio B3 is set to a value capable of increasing the braking force of the vehicle Ve while preventing such a situation. Once the target slip ratio of the wheel 3 during ABS operation is set to the third target slip ratio B3, this flow chart is temporarily terminated.

If the vehicle speed is equal to or lower than the second vehicle speed in step S10, the process proceeds to step S13. When the process proceeds to step S13, the operation of the ABS is prohibited. In other words, since the vehicle speed is equal to or lower than the second vehicle speed, it is determined that the stability of the vehicle Ve will not be excessively reduced due to a decrease in the lateral force of the wheel 3 even if the operation of the ABS is immediately prohibited. Therefore, the operation of the ABS is prohibited, and this flowchart is temporarily terminated.

If the answer in step S2 is negative because no earthquake has occurred, the process proceeds to step S14, where the ABS is permitted to operate. After that, the process proceeds to step S15, where the target slip ratio when the ABS is activated is not changed from the reference target slip ratio B0, and this flow chart is temporarily terminated.

According to the control in yet another example configured in this way, when an earthquake occurs, the target slip ratio of the ABS is changed according to the current vehicle speed. Specifically, when the vehicle speed is high, the increase in the target slip ratio is reduced, and as the vehicle speed decreases, the increase in the target slip ratio is increased. Then, when the vehicle speed becomes lower than the second vehicle speed, the operation of the ABS is prohibited. Since the stability of the vehicle Ve decreases when the vehicle speed is high, the target slip ratio is set so that the lateral force of the wheel 3 does not decrease excessively, and when the vehicle speed decreases, the target slip ratio is increased to increase the braking force. Therefore, when an earthquake occurs, the stability of the vehicle Ve is ensured, the wheels 3 are prevented from locking, and the vehicle Ve can be stopped quickly.

2 Brake device 3 Wheel 4 ECU (controller)
4b Earthquake Judgment Section

Claims (1)

Wheels and
A brake device that applies a braking torque to the wheel;
an antilock brake system that controls a braking torque of the brake device so that a slip ratio of the wheel with respect to a road surface becomes a predetermined reference target slip ratio,
a controller for controlling the brake device and the antilock brake system;
The controller:
An earthquake determination unit is provided to detect the occurrence of an earthquake,
A vehicle control device characterized in that, when the earthquake judgment unit detects the occurrence of an earthquake, the vehicle is configured to prohibit operation of the anti-lock brake system, or to set a corrected target slip ratio that is greater than the standard target slip ratio and activate the anti-lock brake system.

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